Update README.md

Changed the repository to Github instead of mech.kuleuven.be
* commented out check for authenticated shibboleth session in the request before proceeding handling the request by the shibboleth firewall listener
* fixed logout handler to also use the optional return url argument if no idp logout url is found in the request
Merge pull request #3 from bramcordie/patch-1

Update README.md
Ckeck for a value in Shib-Identity-Provider header
Merge pull request #4 from jchampion/master

Ckeck for a value in Shib-Identity-Provider header
Load user from token, not from username
ShibbolethUserProviderInterface now includes loadUser($token) method
AbstractShibbolethUserProvider includes simple implementation of loadUser($token)

This modification enables updating user object (stored elsewhere) with data from shibboleth headers